The prior art filter apparatus having a bag unit with a resilient gasket is described in U.S. Pat. No. 5,075,004, issued Dec. 24, 1991. Related patents include U.S. Pat. Nos.:
U.S. Pat. No. 3,771,664, issued Nov. 13, 1973, PA1 U.S. Pat. No. 4,133,769, issued Jan. 9, 1979, PA1 U.S. Pat. No. 4,204,966, issued May 27, 1980, PA1 U.S. Pat. No. 4,259,188, issued Mar. 31, 1981, PA1 U.S. Pat. No. 4,285,814, issued Aug. 25, 1981, PA1 U.S. Pat. No. 4,419,240, issued Dec. 6, 1983, PA1 U.S. Pat. No. 4,460,468, issued Jul. 17, 1984, PA1 U.S. Pat. No. 4,842.739, issued Jun. 27, 1989, PA1 U.S. Pat. No. 4,490,253, issued Dec. 25, 1984, PA1 U.S. Pat. No. 4,669,167, issued Jun. 2, 1987, and PA1 U.S. Pat. No. 5,039,410, issued Aug. 13, 1991.
The prior art filter apparatus generally have a bag with a resilient gasket including a housing, a cover plate, a basket, and a bag filter subassembly. The bag filter subassembly has a bag composed of filter material such as paper or cloth and a resilient seal member. The filter bag is conventionally a three-layer bag unit, which has a first inner layer, a second middle filtration layer, and a third spun fiber outer layer.
One of the major problems with the prior art filter apparatus is that it is difficult to remove the bag filter subassembly, when loaded, due to locking or bonding of the three-layer bag unit to the perforations in the metal basket holder. This occurs because the filter material bag, due to the pressure of the liquid flow, forces the filter material into the outlet holes or mesh of the basket. Considerable force is required to free the bag which can result in the rupturing of the bag and the contamination of the line.
Another problem is that the filters bags are difficult to manufacture because the outer layer is easily damages and this same condition prevails in packaging and shipping, as well as during installation.
A further problems with the prior art filter apparatus is that fiber shedding can occur from the outer surface of the third layer as this surface because it can be easily damaged. This results in fibers migrating into the clean filtrate with the resulting contamination.